The present invention relates generally to friction clutches, and in particular to a clutch assembly used in high performance vehicles such as racing cars.
As is well known, vehicle clutches operate to selectively couple and decouple an engine to a drive shaft for the purpose of starting the engine while the vehicle is in gear, bringing the vehicle to a stop while the engine is running, changing gears while the vehicle is in motion and putting the vehicle in motion from a dead stop. Conventional clutches include a cover assembly having an annular cover plate and at least one annular pressure plate connected to the cover plate for conjoint rotation with the cover plate. The cover plate is fixedly attached to a flywheel driven by the vehicle engine, so that the pressure plate is located between the cover plate and the flywheel. Typically, attachment of the cover plate to the flywheel is by a plurality of threaded fasteners received in spacers between the flywheel and the cover plate. The spacers engage the peripheral edge of the pressure plate causing the conjoint rotation of the flywheel, cover plate and pressure plate.
A driven shaft is received through the cover assembly and flywheel free of fixed connection to any of these so that absent action of the clutch, the driven shaft and flywheel rotate independently of each other. The driven shaft is splined and one or more friction discs are mounted on the splines for conjoint rotation with the driven shaft, while being free to slide longitudinally of the driven shaft. The friction discs are positioned between the pressure plate and the flywheel. Floater plates are disposed between adjacent friction discs and also rotate with the spacers.
Springs between the cover plate and the pressure plate force the plate away from the cover plate and clamp the friction discs against the flywheel. This clamping action mates the drive shaft and flywheel for conjoint rotation so that the drive shaft is driven by the engine. The clutch is released to permit independent rotation of the flywheel and drive shaft by a clutch pedal in the vehicle connected to the pressure plate by a mechanical linkage.
The spacers that engage the periphery of the pressure plate typically comprise a round sleeve that contacts each pressure plate at a single contact point. When the spacers wear, grooves will form on the external surface of the spacer as a result of the high concentration of forces transmitted through the single contact point of each spacer. During operation of the vehicle, the axial movement of the pressure plates is inhibited by the grooves formed on the spacers causing the clutch to stick. Therefore, a need exists to extend the wear life of the spacers and improve operation of existing clutch designs.
As the vehicle operates, the cover plate endures bending forces that cause deflection of the cover plate. The cover plate deflection results in fatigue and eventual failure of the cover plate. Typically, the cover plate is strengthened by making it of steel and sizing it large enough to resist the bending forces. Increased size and weight of the cover plate undesirably increases its inertia. In high performance racing, a stock car may operate at 8,000 to 9,000 rpm for several hours to complete a race. The inertia of the cover plate becomes a hindrance to racing performance because of the energy from the engine taken up to maintain rotation of the cover plate detracts from the speed of the car. Therefore, it is desirable to construct a cover plate that is lightweight but has sufficient strength to withstand the bending forces present under racing conditions.